In heart surgery and the like, an artificial heart-lung machine is used to take over the respiratory function and the circulatory function of a patient under going the surgery. Moreover, during the surgery, in order to reduce the oxygen consumption by the patient, it is necessary to lower the patient's body temperature and maintain the lowered body temperature. For this purpose, the artificial heart-lung machine is equipped with a heat-exchanging portion and thereby controls the temperature of blood taken from the patient.
Now, the configuration of a conventional example of an artificial heart-lung machine will be described using FIG. 14. FIG. 14 is a cross-sectional view schematically showing the configuration of a conventional example of an artificial heart-lung machine. This artificial heart-lung machine includes a heat-exchanging portion (heat exchanger) 130 that performs blood temperature control and a gas-exchanging portion (artificial lung) 131.
The heat-exchanging portion 130 and the gas-exchanging portion 131 are accommodated in a housing 122. A cold/warm water supply port 123 for introducing cold/warm water for heat exchange and a cold/warm water discharge port 124 for discharging the cold/warm water are provided in a segment of the housing 122 corresponding to the heat-exchanging portion 130. A gas supply port 125 for introducing oxygen gas and a gas discharge port 126 for discharging carbon dioxide and the like in blood are provided in a segment of the housing 122 corresponding to the gas-exchanging portion 131.
The heat-exchanging portion 130 includes a plurality of metal tubes 101 arranged parallel to one another within a housing 102. Each tube 101 communicates with the cold/warm water supply port 123 and the cold/warm water discharge port 124, and cold/warm water flows through the interior of the tube 101. Moreover, an inlet port 106 for introducing blood removed from a patient is provided in an upper face of the housing 102. Blood that has undergone heat exchange in the heat-exchanging portion 130 flows toward the gas-exchanging portion 131.
Moreover, a sealing member 103 (shown with dots by hatching in the areas where the sealing member 103 is formed) is provided within the heat-exchanging portion 130. The sealing member 103 seals the blood flowing within the heat-exchanging portion 130 while coming into contact with the surface of the tubes 101, thereby forming a blood channel 108 for the blood introduced from the inlet port 106. The sealing member 103 is formed by filling spaces between the tubes with a resin material in such a manner that opposite both open ends of the plurality of tubes 101 are not blocked.
The gas-exchanging portion 131 is formed by laminating a plurality of hollow fiber sheets 105. The hollow fiber sheets 105 are formed by bundling a plurality of hollow fibers with lateral yarns. A sealing member 104 (shown with dots by hatching in the areas where the sealing member 104 is formed) is also provided within the gas-exchanging portion 131. The sealing member 104 seals the blood flowing within the gas-exchanging portion 131 while coming into contact with the surface of the hollow fibers constituting the hollow fiber sheets 105, and thereby forms a blood channel 113 within the gas-exchanging portion 131.
The sealing member 104 is formed by filling spaces between the hollow fibers with a resin material in such a manner that opposite open ends of the hollow fibers constituting the hollow fiber sheets 105 are not blocked. The gas supply port 125 and the gas discharge port 126 are in communication with each other through the hollow fibers constituting the hollow fiber sheets 105.
With the above-described configuration, blood passing through the blood channel 108 in the heat-exchanging portion 130 while exchanging heat flows into the blood channel 113 in the gas-exchanging portion 131, so as to come into contact with the hollow fibers. At this time, oxygen gas flowing through the hollow fibers is taken in by the blood. The blood that has taken in the oxygen gas is discharged to the outside from a blood outlet port 107 provided in the housing 122, and returned into the patient. On the other hand, carbon dioxide in the blood is taken in by the hollow fiber sheets 105 and then discharged from the gas discharge port 126 to the outside of the artificial heart-lung machine.
Moreover, in the case where an artificial heart-lung machine is used, in order to remove air and foreign matter from a blood circuit and allow the hollow fibers of the gas-exchanging portion 131 to acclimatize to liquid, priming is performed beforehand using a priming liquid such as a physiological saline solution, and blood circulation is performed thereafter. However, even when priming has been performed, air may mix into the blood during the blood circulation, and so it is required to equip the artificial heart-lung machine with a function for removing air. With such a function, priming can be finished in a short period of time, which is effective in medical emergencies. Thus, various artificial heart-lung machines equipped with a function for removing air have been proposed conventionally (see Patent Documents 1 to 3).
For example, an artificial heart-lung machine disclosed in Patent Document 1 uses hollow fibers as the tubes of a heat-exchanging portion. A side wall of the hollow fibers is formed of a porous membrane and a thin film of silicone rubber covering the exterior of the porous membrane, and is permeable only to gas. Moreover, in this artificial heart-lung machine, the pressure of cold/warm water flowing inside the hollow fibers is set to be lower than the pressure of blood flowing outside the hollow fibers. This allows air in the blood to be taken into the interior of the hollow fibers through the side wall of the hollow fibers and separated from the blood.
According to the artificial heart-lung machines disclosed in Patent Documents 2 and 3, a heat-exchanging portion has a plurality of metal tubes, but unlike the example in FIG. 14, blood flows through the interior of the tubes and cold/warm water flows over the surface of the tubes. Moreover, the heat-exchanging portion includes, on an entrance side of the tubes, a space for temporarily storing blood and an inlet port that causes the blood to flow into the space while swirling.
In the heat-exchanging portion of the artificial heart-lung machines of Patent Document 2 and 3, blood and air are separated from each other by a centrifugal force caused by the swirling of the blood, and only the blood from which air has been removed is transferred into the tubes of the heat-exchanging portion. Furthermore, in Patent Document 3, the heat-exchanging portion includes another space for temporarily storing blood on an exit side of the tubes, and a valve through which this space can communicate with the outside is provided in a wall face of this space. With the heat-exchanging portion of Patent Document 3, air is removed more reliably.    Patent Document 1: JP 8-24333 A    Patent Document 3: JP 11-47269 A    Patent Document 2: JP 6-14965 B